1. Field of the Invention
The present invention relates to a passive safety device for a vehicle having a safety unit such as an air bag or the like, and especially, to a backup capacitor capacity detecting device for detecting the capacity of a backup capacitor used for the passive safety device for a vehicle.
2. Description of the Related Art
In general, a passive safety device for a vehicle for protecting a passenger by filling out an air bag or the like when a vehicle collides with something is provided with a backup capacitor for the purpose of actuating the passive safety device for a vehicle even if a vehicle battery is brought in an unusable state by a break of a wire in the occurrence of collision. In order to successfully actuate the passive safety device for a vehicle by the backup capacitor, it is necessary to check whether the capacity of the backup capacitor (amount of charge) is working normally or not. For this reason, a conventional passive safety device for a vehicle is provided with a backup capacitor capacity detecting unit.
As a backup capacitor capacity detecting unit as above, for example, a xe2x80x9ccapacitor capacity diagnosing circuitxe2x80x9d disclosed in Japanese Patent Publication No. 9-229976 is known.
FIG. 5 is a block diagram showing a conventional backup capacitor capacity detecting unit used for conventional passive safety device for a vehicle. Referring to FIG. 5, a reference numeral 1 denotes an on-board battery; a reference numeral 2 an ignition switch; a reference numeral 10 a reverse current blocking diode; a reference numeral 11 a processing circuit; a reference numeral 12 a switching transistor; a reference numeral 31 a power source circuit; and a reference numeral 32 a backup capacitor. The power source circuit 31 is, for example, a DCxe2x80x94DC converter for boosting the voltage of the on-board battery 1 to a predetermined one. The reverse current blocking diode blocks flowing of charges accumulated in the backup capacitor 32 into the power source circuit 31 in the occurrence of a failure of the power source circuit 31. The processing circuit 11 diagnoses the failure of the backup capacity, as described below.
Next, the operation of the conventional backup capacitor capacity detecting unit will be described.
When the ignition switch 2 is closed, the on-board battery 1 is charged up by charges migrated from the backup capacitor 32 via the power source circuit 31. In making a diagnose the capacity of the backup capacitor 32, it is enough to turn on the switching transistor 12, which discharges the charges accumulated in the backup capacitor 32 via a resistor R2 and the switching transistor 12. On the other hand, the terminal voltage of the backup capacitor 32 is applied to the processing circuit 11 by dividing the terminal voltage by resistors R3 and R4. Thus, the processing circuit 11 measures a voltage drop caused by the discharge of the backup capacitor 32 and detects the capacity (amount of charge) of the backup capacitor 32 based on the voltage drop.
A backup capacitor capacity detecting unit for a conventional passive safety device for a vehicle is configured in the manner described above. Thus, when detecting the capacity of the backup capacitor, a switching transistor needs to be turned on to forcibly discharge the backup capacitor, which precludes the use of the backup capacitor in the course of the detection of the capacity of the backup capacitor.
Further, the conventional passive safety device for a vehicle is separately provided with the backup capacitor capacity detecting unit. In other words, it demands a switching transistor and a processing circuit for detecting the capacity of the backup capacitor, and thus the cost of the passive safety device for a vehicle will be expensive.
The present invention has been made to solve the above problems described above, and an object of the present invention is to provide a passive safety device for a vehicle, which is able to use a backup capacitor even in the course of the detection of the capacity of the backup capacitor. Another object of the present invention is to provide an inexpensive passive safety device for a vehicle.
A passive safety device for a vehicle according to the present invention comprises a passive safety unit for protecting a passenger ridden in a vehicle; an ignition circuit, connected to an on-board power source, for applying an operating current to the passive safety unit to actuate the passive safety unit; a backup capacitor, connected to the on-board power source and the ignition circuit, for applying the operating current to the passive safety unit when the ignition circuit is disconnected from the on-board power source; a control part, connected to the on-board power source via the backup capacitor, for controlling the ignition circuit; and a nonvolatile memory in which failure diagnosis information is stored, wherein the control part has first means for writing predetermined data in the nonvolatile memory after a predetermined time has elapsed when the on-board power source is turned off; and second means for reading the predetermined data written in the nonvolatile memory, when the on-board power source is turned on, for judging whether the predetermined data is written in the nonvolatile memory or not, and for determining the backup capacitor not to be working normally if the judgement shows that the predetermined data is not written in the nonvolatile memory.
In the passive safety device for a vehicle according to the present invention, the predetermined time is shorter than the operating time of the control part defined by the discharge time of the backup capacitor when the backup capacitor is working normally, and is longer than the operating time of the control part defined by the discharge time of the backup capacitor when the backup capacitor is not working normally.
In the passive safety device for a vehicle according to the present invention, the predetermined time is determined on the basis of a result obtained by measuring the operating time of the control part of each device, and is written in the nonvolatile memory.
A passive safety device for a vehicle according to the present invention comprises a passive safety unit for protecting a passenger ridden in a vehicle; an ignition circuit, connected to an on-board power source, for applying an operating current to the passive safety unit to actuate the passive safety unit; a backup capacitor, connected to the on-board power source and the ignition circuit, for applying the operating current to the passive safety unit when the ignition circuit is disconnected from the on-board power source; a control part, connected to the on-board power source via the backup capacitor, for controlling the ignition circuit; and a nonvolatile memory in which failure diagnosis information is stored, wherein first data and second data different from the first data are written previously as initial values in the nonvolatile memory, and wherein the control part has first means for comparing the first data with the second data, when the on-board power source is turned on, and for judging the backup capacitor not to be working normally, if the first data coincides with the second data, and for applying a predetermined processing to the first data to make the first data equal to the second data and for writing the first data in the nonvolatile memory; and second means for applying a predetermined processing to the second data after a predetermined time has elapsed to make the first data unequal to the second data, when the on-board power source is turned off and for writing the second data in the nonvolatile memory.
In the passive safety device for a vehicle according to the present invention, the predetermined time is shorter than the operating time of the control part defined by the discharge time of the backup capacitor when the backup capacitor is working normally, and is longer than the operating time of the control part defined by the discharge time of the backup capacitor when the backup capacitor is not working normally.
In the passive safety device for a vehicle according to the present invention, the first data and the second data have the same bit length, and wherein the first means and the second means rotate the first data and the second data by a predetermined number of bits, respectively.
In the passive safety device for a vehicle according to the present invention, the first data is equal to xc2xd of the second data, and wherein the predetermined number of bits is one.
In the passive safety device for a vehicle according to the present invention, the first data has a plurality of first comparing data and the second data has a plurality of second comparing data, each corresponding to the first comparing data, and wherein the first means and the second means perform a predetermined processing for each of the first comparing data and the second comparing data, respectively, and wherein the first means compares the first data with the second data for each of the first comparing data and the second comparing data, and judges the backup capacitor not to be working normally if the judgement shows that the number of comparing data coincided with each other surpasses a predetermined number.
In the passive safety device for a vehicle according to the present invention, the first means judges the backup capacitor not to be working normally if the first data and the second data written in the nonvolatile memory coincide with each other as many as a predetermined number of times.
In a passive safety device for a vehicle according to the present invention, the predetermined time is determined on the basis of a result obtained by measuring the operating time of the control part for each device, and is written in the nonvolatile memory.
The above and other objects and the attendant advantages of the invention will become readily apparent by referring to the following detailed description o f the preferred embodiments when considered in conjunction with the accompanying drawings.